Directional solidification of aluminium-silicon eutectic alloys were carried out in order to investigate the mechanism by which the quench modification takes place. For this purpose a new type of Bridgman furnace was designed which can attain a high temperature gradient and a high interfacial growth velocity up to 1000 mu m s(-1). It is established that the fibrous structure is the result of faceted-non-faceted growth of the coarse silicon particle at high solidification rate. It is observed that refining of the flake structure closely follows the characteristics of normal eutectic.